Emulsion polymerization of ethylenically unsaturated monomers in the presence of surface active agents is well known.
A deficiency in the industry has been the inability to balance tile necessary hydrophilicity for effecting emulsion polymerization of the monomers without sacrificing water resistance in the resulting polymer products. Another deficiency is that it has been difficult and costly to incorporate active functionality into emulsion polymers due to copolymerization considerations as well as a lack of chemical versatility in the available functional monomers.
Normally, aqueous polymer emulsions employ hydrophilic polymers such as poly(vinyl alcohol) [PVOH], poly(ethylene oxide), or poly(vinyl pyrrolidone) (PNVP) or surfactants such as alkylphenol ethoxylates, alkyl sulfonates, or alkyl ammonium salts as stabilizers to allow stable polymerization in an aqueous continuous phase. Due to the hydrophilicity of these materials, emulsion polymers prepared containing these materials remain sensitive to the presence of water even after polymers are cast into a solid film, as would be utilized for adhesives, for example. This water sensitivity leads to limitations in the types of applications where these emulsion polymers can be used. Emulsion polymers exhibiting this water sensitivity cannot typically be used, for example, in outdoor applications where exposure to the elements would cause degradation of polymer performance and ultimately in failure of the polymer product.
Previous solutions to water sensitivity have involved incorporation of functional monomers into the emulsion polymers themselves where they remain until catalyzed or promoted to reaction by some mechanism. Typical monomers of this type are N-methylolacrylamide, hydroxyethyl acrylate, glycidyl (meth)acrylate and similar monomers. Several technical problems limit the utility of these types of monomers in addition to economic considerations. Such hydrophilic monomers are soluble in water and are therefore difficult to incorporate effectively into emulsion polymer compositions. Polymerization of these monomers in the aqueous phase can result in serious difficulty in controlling the viscosity of the dispersion and can lead to inadequate performance as crosslinking agents. Consideration also must be given for the differing reactivities of the monomers in the system. These reactivity considerations can affect the available compositions for the individual monomers in the overall product as well as the distribution of the dissimilar monomers within the polymer molecules.
The following patents describe emulsion polymerization of vinyl acetate, vinyl chloride and vinylidene chloride and their copolymers with ethylene or acrylates.
U.S. Pat. No. 5,011,883 discloses copolymers of vinyl monomers such as vinyl acetate and acrylates incorporating PVOH into the emulsion product. This approach has limitations with respect to the level of vinyl acetate which can be homogeneously incorporated into the emulsion product and with respect to properties such as glass transition temperature (Tg). The latter is due to copolymerization of the vinyl monomer with the acrylic monomers.
EP 0,489,524 describes the preparation of amine containing emulsion products which incorporate amine functionality through the use of ammonium salts of fatty acids which are subsequently decomposed at elevated temperatures to produce acid functionality and ammonia. In that case, the conversion of the ammonium functionality used for stabilization to the thermalized acid form results in the transformation of the compound from the water soluble to a water insoluble species.